Optical storage media are media in which data is stored in an optically readable manner, so that they can be read, for example, by means of a laser and a photodetector being integrated in a pickup. Current generation commercial optical storage media include single- and dual-layer DVD and Blu-ray discs, in which recording and playback are based on controlling or detecting returned light from reflective layers within the medium (i.e. an optical disc). Of these, the highest data storage capacity, and greatest longevity, is achieved by Blu-ray discs, which can contain up to about 50 gigabytes of information, while some manufacturers produce ‘archival quality’ media with claimed lifespans of 50-100 years.
Long-term data recording and preservation, or ‘long data’, is a growing concern in a number of fields. For example, some datasets have a prominent temporal context over long period of time in order to capture and study changes in the world. In astrophysics, biology, geography and social science, datasets accumulated over decades, or even more than a century, have been used to study and analyse phenomena such as climate changes, mutation and global warming. Archiving and preserving information for the future generations is an equally important social obligation. To provide such long data storage, new data storage systems providing high longevity of both recorded and unrecorded regions of the storage media, and high capacity, will be required.
The timescales of long data require storage media with a lifetime of many human generations, e.g. of 100 years and beyond. Furthermore, consideration of physical storage requirements, as well as the size of some long-term datasets of interest, suggests the need for capacities of multiple terabytes per disk. For example, in biology a huge amount of information is being produced, such as the digital data representing a full-sequenced human genome which amounts to about 3.2 gigabytes. Accordingly, to study mutations in the genome of just one family over multiple generations, the accumulated digital data may easily amount to multiple terabytes over a century or more.
Accordingly, there is a demand for new high-capacity mass storage systems and media that are reliable, stable over long time periods, and cost-effective. Furthermore, when used for the accumulation of datasets in long-term data-gathering applications, media should be robust to ongoing use for recording, in contrast to archival media which generally are used only once for recording before being stored under controlled conditions, and only rarely retrieved for read-only use.
Embodiments of the present invention are therefore directed to meeting one or more of the requirements for high longevity, high data storage density and robustness required of optical media in long data storage applications.